1. Field of the Invention
The present invention relates to a method of preprocessing of the process to form a multilayered metal film which becomes an underlayer of a bump which is a part of the manufacturing process of a flip chip IC in which a bump consisting of a metal is formed at the surface of a semiconductor base material through surface contact with an electrode formed at the surface of a printed circuit board.
2. Description of the Related Arts
It is a very important point for further progress in reducing the size of electronic devices to improve a part loading capacity. In regard to a semiconductor IC, development of a high density loading technique by introduction of a flip chip in place of the conventional package loading has been pursued with maximum effort.
A flip chip loading method is classified into several methods such as the Au stud bump method and the solder ball bump method, etc., and a barrier metal is used, in any method thereof, between an electrode pad and the bump material of the semiconductor IC in order to improve close contact and to prevent mutual diffusion therebetween. In the case of the solder ball bump, this method is called a BLM (Ball Limiting Metal) from the point of view that such barrier metal plays a role of deciding the final shape of the bump. The typical structure of a BLM film in the solder bump method, has the three-layer structure of Cr, Cu and Au. The Cu layer as the under layer works as a layer being in contact with an electrode pad, while the Cu layer as a layer preventing diffusion of solder and the Au metal layer as the upper layer works as a layer preventing oxidation of the Cu. As a patterning method of the BLM film, there is provided a wet etching method using chemicals, but this method has a problem of workability, a problem in the environmental and hygienic aspects such as waste fluid processing and a problem that processing accuracy is bad. Therefore, as part of the patterning method of a BLM film, it is also discussed to introduce the lift-off process in which a photoresist film is deposited and thereafter it is lifted off. In this case, the BLM film is generally formed by a sputtering apparatus but it tends to be formed up to the side wall surface of the resist pattern as the under layer. Thereby, the resist remover does not penetrate at the lift-off time, making it difficult to remove the unwanted BLM film. Therefore, it is required for improvement of lift-off characteristic in the lift-off work to control the shape of the end surface of the photoresist aperture to have an overhang area. As a method of controlling the shape of the resist, it can be realized by modification of the lithography process, but this method has a problem in that the number of processes increases and therefore it is an ideal method that the shape of resist pattern is simultaneously controlled in the plasma irradiation process which is usually performed in the preprocessing of the BLM film sputtering. In the related arts, the RF parallel flat plate type plasma processing apparatus as shown in FIG. 8 has generally been used for plasma irradiation process which is performed before formation of a metal film. In the plasma processing apparatus of FIG. 8, a stage (cathode plate) 3 loading thereon a substrate 2 to be processed is positioned within an evacuated plasma processing chamber 14, an anode plate 4 is arranged at the position opposed to the stage and a high frequency power supply 6 is connected to the stage (cathode plate) 3 via a coupling capacitor 5. However, attempts at shape control by the RF etching in this plasma processing apparatus generates a problem that exfoliation in the lift-off process becomes difficult due to some reasons that a single structure of the power supply of the plasma processing apparatus of this type allows only adjustment of the high frequency power which determines density of plasma and the bias voltage which determines ion energy under the predetermined relationship therebetween, low plasma density results in considerable processing time as long as about 5 to 6 minutes, highly preset high frequency power inevitably results in a higher bias voltage which causes the ion energy applied to the substrate to increase, and a thermally changing region extends up to the boundary surface for the lower layer exceeding the surface layer of resist bringing about the condition that the burned resist is stuck to the lower layer.